This invention relates to a fixing device for use in an electrophotographic apparatus such as copying machine or printer.
In conventional electrophotographic apparatus, a light information corresponding to an object to be photographed is caused to illuminate a photosensitive element in the form of a rotary drum, for example, and an electrostatic latent image formed on the photosensitive element is developed into a toner image during a developing step. The toner image is then transfer printed onto a copying medium in the form of a sheet of paper or a resin film under an electric pressure, preferably by using a corona discharger. The copying medium which has been transfer printed with the toner image is separated away from the photosensitive element and then introduced into a fixing device through a guide plate or the like where the toner image on the copying medium is fixed. Generally, the fixing device is constituted by a fixing roller, an electric heating element contained in the fixing roller or disposed adjacent to the peripheral surface thereof, a pressure applying device in the form of rollers or an endless belt which conveys the copying medium while clamping the same between the pressure applying medium and the fixing roller, and such associated members as a peel off pawl and delivery rollers disposed about the fixing roller to cooperate therewith. The prior art fixing device has been incorporated into the electrophotographic apparatus, or constructed as a unitary unit to be removably incorporated into the electrophotographic apparatus.
For this reason, with the prior art fixing device, when the copying medium that is copying paper is jammed in the fixing device, such jammed copying paper cannot be removed readily. Moreover, the prior art fixing device accompanies such trouble as requiring considerable manual operations snd time for exchanging, inspecting and repairing the component elements of the fixing device and for exchanging offset preventing oil.
Moreover, when an endless belt is used for urging the copying paper agaisnt the fixing roller, although there is an advantage that the heating temperature and pressure can be made relatively low since the interval in which the endless belt is urged against the fixing roller is relatively long, there is another defect that since the pressure applied to the fixing roller is not uniform, portions which are unsatisfactorily fixed are liable to be formed.
Furthermore, since the endless belt tends to move transversely or to move in a wave form, not only the belt is broken but also the transfer copying medium, that is the copying paper is wrinkled, thereby forming portions not satisfactorily fixed.